An NMR device comprises a probe comprising a sample holder made to spin in a static magnetic field and exposed to a second magnetic field perpendicular to the first, for example created by a radiofrequency coil, which in return receives a signal which is analysed in order to deduce therefrom information about a sample, notably a solid sample, placed in the sample holder. According to an embodiment of the prior art, three streams of gas coming from one and the same source, a standard container such as a raised-pressure helium cylinder, are directed towards the probe of the device which comprises the sample holder. The first stream has the function of spinning this sample holder, by acting on the blades or vanes of a turbine that drives a rotor (or spinner) which comprises the sample holder. The second stream has the function of bringing the sample to a certain temperature, and the third stream creates an aerostatic bearing that supports the rotor in the stator.
In such a device, it is important to eliminate the risk of atmospheric gases condensing on the probe in the event of low-temperature operation and to define a probe design that guarantees that the ad hoc temperature can be obtained at the sample holder.
There are various conditions that need to be met in order to achieve this:                The probe needs to be insulated from the surrounding atmosphere in order to protect it from the condensation and convection of gas in order to eliminate the introduction of heat from outside by convection and as a result of conduction in the gas.        The probe, the spinner and the device supplying it with fluid need to be protected from the surrounding thermal radiation at a temperature of around 300K.        
Because the probe and, more extensively, the NMR device, operate at a very low temperature, it is necessary to lag these in order to achieve the desired temperatures and/or in order not to consume excessive amounts of energy in order to cool them.
There are various known techniques for lagging or insulating a cooled device, notably:                surrounding it in insulating materials that make it possible to avoid losses by convection or even by conduction, or        the placement of radiation-impeding screens that make it possible to avoid losses by radiation.        
The temperature of a radiation-impeding screen is influenced by the “hot” components and the “cold” components that face the screen. This influence varies with the fourth power of the difference in temperature of the hot components and the cold components, the temperature of the screen being influenced mainly by the “hot” components, particularly when operating at very low temperature.